With respect to their outer shape, most of today's hearing devices are in full or in part individually adapted to the shape of the ear of the individual wearing the hearing device, in particular to the shape of the ear canal and/or of the concha. BTE (behind the ear) hearing device comprise an ear mold, which is individualized, and in case of ITE (in the ear) hearing device, in particular ITC (in the canal) and CIC (completely in the canal) hearing devices, at least a portion of the shell or housing of the hearing device is individualized. For a proper function of a hearing device and for a comfortable wearing experience of the hearing device user, it is necessary to precisely reproduce the shape of the ear canal and/or concha, typically within fractions of a millimeter.
For this individualization, usually ear impressions in silicone are made by applying viscous silicone to the outer ear and the ear canal. After curing of the silicone and removal from the ear, the shape is three-dimensionally scanned for building a shell on basis of so-obtained scanning data, or it is used for forming a negative, by means of which a (positive) shell is then created.
Taking such silicone impressions is a very delicate process, as it requires special skills and depends on various parameters.
Therefore, an improved reproducibility is desirable, as well as a simplification of process steps to be carried out by persons involved.
Several non-contact measuring techniques have been described in the art.
WO 02/21894 A2 describes a non-contact optical method for reconstructing the shape of the inner surface of an ear canal, in which video signals from inside the ear canal are recorded and analyzed. This analysis yields position data of said inner surface, based on which hearing device shells can be manufactured.
Another optical non-contact measurement method for ear canals is disclosed in WO 02/16867 A1. In this case, structured light is projected onto the surface to be measured. The so-obtained pattern is imaged by a camera and analyzed, so as to yield the desired three-dimensional shape.
Yet another optical non-contact measurement method for ear canals is disclosed in WO 02/091920 A1. In this case, light is directed at the inner ear canal surface to be measured. The reflected light is detected and analyzed with respect to its light path (angle and/or position). By means of geometrical methods (triangulation), the distance of the probe to the ear canal surface can be obtained.
Due to the relatively low absorption of light in the human skin (epidermis, dermis), a halo of considerable intensity and size is created near incident light (due to volume scattering in the epidermis, dermis), so that the above-described non-contact optical methods tend to yield results of insufficient accuracy, at least unless the skin is specifically prepared, e.g., by covering it with talcum powder.
It is desirable to create an alternative method and system for reconstructing the three-dimensional shape of the surface of at least a portion of an ear canal and/or of a concha, in particular a method and system providing for an increased accuracy and/or reproducibility.